The present invention relates to the art of earth boring and, more particularly, to a system for continuously lagging a tunnel formed by an earth boring machine.
During the boring of a tunnel, serious problems are often encountered because portions of the roof behind the cutterhead tend to cave onto the tunneling machine and into the area behind the tunneling machine, damaging equipment and creating a substantial hazard for personnel in the area. In order to overcome this problem, lagging consisting of short lengths of timber, sheet steel, concrete slabs, or the like are used to secure the roof. This lagging forms a permanent roof support and protects personnel and equipment behind the tunneling machine. The lagging may be in the form of a solid layer of material, or it may be what is known as finger lagging, wherein substantial gaps are located between adjacent sections of lagging.
Prior to applicant's present invention the rock and earth formations above the roof of the tunnel between the cutterhead and the lagging in place were unsupported and would tend to fall onto the machine or into the tunnel behind the machine. In addition, prior to applicant's present invention, personnel installing the lagging had to venture into an area where the roof was not supported. It is difficult to provide lagging directly above the tunneling machine while drilling is in progress. Thus, there is a danger of rock and portions of the formations falling from the crown of the tunnel onto the machine or on workers operating the machine and/or attempting to put lagging in place. Some tunneling machines have included shields above the machine body; however, the area between the end of the shield and the lagging in place is unsupported.
The present invention overcomes these problems by providing a continuous lagging system that will operate effectively while drilling is in progress. The operating personnel and machinery are provided with continuous protection from broken ground falling out of the tunnel roof. Permanent roof support systems are installed behind the machine and the invention affords continuous protection for the workmen installing the permanent roof support structures. The invention eliminates the danger zone just behind the cutterhead to the first permanent roof support by providing a smooth transition of roof load from the machine rock shield to the tunnel support rings.